1. Field of the Invention
The present disclosure relates to droplet ejection apparatuses and methods for ejecting liquid droplet.
2. Description of the Related Art
For example, an inkjet recording apparatus is known as an image forming apparatus including a printer, a fax machine, a copy machine, and a multifunction peripheral. The inkjet recording apparatus forms a desired image on a recording medium such as a paper sheet and a film for OHP (overhead projector) by ejecting droplets from an inkjet recording head.
As the inkjet recording head, so called piezoelectric type recording head is known, in which a piezoelectric element is used for pressuring ink in an ink flow channel. A vibration plate forming wall of the ink flow channel is vibrated with the piezoelectric element so as to change a volume inside the ink flow channel, thereby ejecting the ink droplets.
Recently, operation speed of the inkjet recording apparatus using the recording head as described above is improved. Also, a line-scanning-type inkjet recording apparatus, with which high speed operation can be achieved, is proposed. There are line scanning inkjet type recording apparatuses including a continuous inkjet recording heads and line scanning inkjet recording apparatuses including on-demand inkjet recording heads. The operation speed of the inkjet recording apparatus including the on-demand inkjet recording head (e.g., Japanese Unexamined Patent Application Publication No. H11-78013) is lower in comparison to the inkjet recording apparatus including the continuous inkjet recording head. However, the inkjet recording apparatus including the on-demand inkjet recording head is preferable for widely distributed high speed recording apparatus because the ink system can be made simple.
When drive frequency of the recording head is increased in order to achieve the high speed operation of the recording apparatus, an interval of droplet ejection decreases. In this case, a droplet ejection operation starts before a meniscus vibration caused by a preceding droplet ejection operation decays sufficiently, because of the decreased interval of droplet ejection. Therefore, impact positions of droplets and amounts of ink in a droplet may disperse to cause a degradation of image quality such as inclined ejection and variation in the density of ink.
Hence, the meniscus needs to be made stable in order to perform a high quality image forming. For example, as illustrated in FIG. 15, a method for stabilizing the meniscus is known, in which a control waveform for suppressing residual vibration is included in a head drive waveform for ejecting the ink droplet (Japanese Unexamined Patent Application Publication No. 2002-337333).
FIG. 15 is a diagram illustrating a head drive waveform including a waveform for ejecting the ink droplet from the head and a waveform for stabilizing the meniscus on a nozzle surface after ejection of the ink droplet. In FIG. 15, P1 to P5 are ejection pulses for ejecting the ink droplet while P6 is a vibration control waveform for stabilizing the meniscus.
However, in a case where the vibration control waveform is included in the head drive waveform, a total length of the head drive waveform becomes long. Therefore, upper limit frequency of head drive operation decreases, and high speed image forming operation becomes difficult in such a state.